Clocks at NIST Boulder in Colorado run faster than NIST Gaithersburg in Maryland by about 1.55 microseconds per year because of the 1500 meter altitude differen

Clocks at NIST Boulder in Colorado run faster than NIST Gaithersburg in Maryland by about 1.55 microseconds per year because of the 1500 meter altitude difference. It's about 1 nanosecond per year per meter. They both have to use a fudge factor to adjust down to sea level.